This invention relates to a modular housing for an electrical meter or metering type instrument, an electrical instrument comprising such a housing and a mounting member therefor. The invention particularly concerns an instrument housing adapted for housing one of a plurality of modular type electrical meter or metering instruments.
Electrical meter or metering instruments are usually provided with a display panel so that readings of the meter or metering instrument can be displayed either in analogue or digital form so that the readings can be read for monitoring recording or other purposes by users of equipment the instrument is being used for. Many meter or metering type instruments are panel mounted, that is to say the display panel at one end of the instrument is mounted in a correspondingly sized aperture in a panel in which several instruments may be mounted. In panel mounted arrangements the display panel is mounted substantially flush with the panel surface, with the main body of the instrument being concealed behind the panel and out of sight of the user. The instrument is typically mounted in a cantilever type manner with the instrument being supported in the aperture and secured to the panel in various ways.
There is an increasing demand for electrical meters or metering type instruments which are read remotely by a remote processor which may be located in a control centre up to 100 metres or more from the instrument. Instruments for this type of application can be designed without a readable display unit allowing cost savings to be made or offset against the additional costs of a communication interface and installation cabling. Typically, electrical meter or metering type instruments that do not have a display screen are mounted differently to the panel mounted instruments with a display. Instruments without a display are usually either surface mounted, including wall mounting, or mounted on a DIN rail in a cabinet.
Hitherto, it has been necessary for instrument manufacturers to design and develop separate ranges of electrical meters or metering type instruments for panel mounted applications, where a display is required, and surface or rail mounted applications where the display can be replaced with a communications interface. This has led to significantly different designs of electrical instruments, with few shared components, for each of the mounting methods concerned. A consequence of the different mounting methods described is that very few components can be shared often because the principle dimensions of the instruments is determined by the method of mounting that is employed. For example, panel mounted instruments have to conform to a standard shape and size so that they fit standard panel apertures, for instance 92 mm×92 mm for one particular standard. This results in different size and shaped housings for the instruments which prevents the use of common electrical components such as PCB's. The PCB's may contain the same discrete electrical components but the size and shape of the instrument determines that the fabrication of these components on the PCB and is usually different for each mounting application. This can have a significant impact on the cost of the instruments since lower production volumes can prevent economies of scale being made.